The invention relates generally to the field of vacuum pumps and compressors. In particular, the present invention relates to radial flow turbomolecular vacuum pumps and methods for operating radial flow pumps.
Prior art vacuum pumping systems are typically continuous flow compression systems that evacuate gas from a vacuum chamber at low pressure, for example 10xe2x88x926 torr, and then compress the gas to atmospheric pressure so that the gas may be discharged to the atmosphere. Such prior art pumping systems would typically include a high vacuum pump, such as a turbomolecular pump or a diffusion pump, capable of evacuating to high vacuum. This pump would be followed by a fore pump such as an oil sealed rotary pump or a diaphragm pump, which would further compress the gas and exhaust the gas to the atmosphere.
Vacuum pumps are used for numerous applications including vacuum based instrumentation, such as mass spectrometers, electron microscopes, and various surface analysis tools that use ion or electron beams. Such vacuum based instruments are typically designed for use in dedicated laboratories because of the size, weight, and service requirements of the vacuum pump and other hardware. Consequently, analysis is typically performed by transporting the material to be analyzed to a dedicated laboratory facility. Unfortunately, not all materials that require analysis can be conveniently transported. There is a significant need for portable vacuum based analysis equipment that can be transported to the location of the analysis.
Attempts to produce portable vacuum based instruments have had only limited success because it is difficult to achieve the required pumping capacity with a compact pump design. Also, some prior art pumping designs, such as diffusion and oil sealed pump designs, are sensitive to operating position and have service requirements that are inconsistent with general requirements for portable pumps. Prior art turbomolecular pumps must have a substantially large axial dimension in order to have acceptable pumping efficiency. Other prior art vacuum pumps, such as diaphragm type pumps, require several compression stages which adds to their size, weight and power requirement.
Many prior art portable instruments use storage-type vacuum pumps. Storage vacuum pumps include ion pumps, getter pumps and sorption pumps. These pumps operate by capturing gas molecules within the pump and storing them. The molecules are stored up to some capacity limit of the pump and then the pump must be discarded or reprocessed, which is both inconvenient and expensive.
Storage-type vacuum pumps have numerous disadvantages. Storage-type vacuum pumps have poor pumping speed for certain gases. They are also difficult to restart after a shutdown. In addition, if the pumps store toxic gases, there is a danger of poisoning the user if the pump malfunctions. Notwithstanding the disadvantages of storage type vacuum pumps, these pumps are only slightly smaller than the compression type pumps.
In addition, laboratory space, especially in the semiconductor industry, is very costly and not easily expandable and reconfigurable. There is also a significant need for compact instruments that reduce the size, weight and service requirements of analysis equipment used in laboratories. In addition, there is a need for compact add-on instruments that do not significantly increase the footprint of existing laboratory equipment so as to avoid reconfiguring a laboratory.
The present invention relates to compact vacuum pumps that can be used in instrumentation where the application may be portable, hand held or space limited. A principal discovery of the present invention is that an efficient compact turbomolecular vacuum pump can be constructed having a radial flow design where the dimension of the gas flow path in the radial direction is greater than the dimension of the gas flow path in the axial direction.
Accordingly, in one embodiment, the present invention features a radial turbomolecular vacuum pump that includes a gas inlet, a gas outlet, a rotor, and a casing. The rotor includes a first rotor surface that is positioned in a substantially radial direction. A first plurality of blades extends from the first rotor surface in a substantially axial direction. In one embodiment, at least one blade of the first plurality of blades is shaped to increase pumping efficiency. A support ring that reduces deflection due to centrifugal force may be positioned around at least one blade of the plurality of blades. The rotor and at least one blade of the first plurality of blades may be integrally formed from one piece of material.
In one embodiment, the first rotor surface may include at least one cavity that is dimensioned to receive and to retain at least one blade of the first plurality of blades. The at least one blade of the first plurality of blades may include a dovetail and the at least one cavity may be adapted to receive the dovetail. The dovetail may be oriented in a substantially radial direction or in a substantially circumferentially direction.
In one embodiment, the casing includes a first stator surface that is positioned proximate to the first rotor surface in the substantially radial direction. In another embodiment, the stator is separate from the casing. A first and second plurality of vanes extend from the first stator surface and generally forms an annulus therebetween for receiving the first plurality of blades. The annulus may be a groove. At least one vane of the first and second plurality of vanes and the first stator surface may be integrally formed from one piece of material. The stator may include at least one cavity that is dimensioned to receive and retain at least one of the vanes of the first and second plurality of vanes.
In one embodiment, a drive shaft is coupled to the rotor and is positioned in the substantially axial direction. A motor is coupled to the drive shaft and rotates the rotor relative to the stator. In another embodiment, the rotor is directly coupled to the motor without the use of a drive shaft. The rotation of the rotor relative to the casing causes gas to be pumped from the gas inlet to the gas outlet. A fore pump such as a mechanical pump is typically coupled to the gas outlet. In one embodiment, a processor is electrically coupled to the motor and to a pressure sensor that is positioned in fluid communication with the pump. The pressure sensor generates a signal that is proportional to a pressure achieved by the pump and the processor generates a signal that controls a speed of the motor in response to the pressure.
In one embodiment, the vacuum pump further includes a second rotor surface that is positioned in a substantially radial direction. A second plurality of blades extends from the second rotor surface in a substantially axial direction opposite that of the first plurality of blades. A second stator surface is positioned proximate to the second rotor surface in the substantially radial direction. A third and fourth plurality of vanes extend from the second stator surface and generally forming an annulus therebetween for receiving the second plurality of blades.
In another embodiment, the rotor and stator further comprise a second stage. The second stage includes a rotor surface that is positioned in a substantially radial direction. A plurality of blades extends from the rotor surface in a substantially axial direction. The second stage includes a stator surface that is positioned proximate to the second stage rotor surface in the substantially radial direction. A first and second plurality of vanes extend from the stator surface of the second stator and generally form an annulus therebetween for receiving the plurality of blades.
The present invention also features a method for pumping a gas that includes the step of rotating a plurality of substantially axially disposed blades relative to a first and second plurality of vanes that generally form an annulus therebetween for receiving the first plurality of blades. The relative motion of the plurality of blades and the first and second plurality of vanes causes gas to be pumped in a substantially radial direction from a gas inlet to a gas outlet. The gas may be pumped outwardly or inwardly in a substantially radial direction.
In one embodiment, method for pumping a gas further includes rotating a second plurality of substantially axially disposed blades relative to a third and fourth plurality of vanes that generally form an annulus therebetween for receiving the second plurality of blades. The relative motion of the second plurality of blades and the third and fourth plurality of vanes causes gas to be pumped in a substantially radial direction from a gas inlet to a gas outlet. The gas may be pumped outwardly or inwardly in a substantially radial direction.